1. Field of the Invention
The present invention relates to battery checkers for checking the performance of batteries under simulated load. In particular it relates to a battery checker having an automatic timer for disconnecting the battery from the simulated load a predetermined length of time after the check has commenced.
2. Description of the Prior Art
It is well known to employ a battery checker for checking the condition of the batteries that power the motors and circuits in such portable apparatus as photographic cameras, movie cameras, tape recorders, etc. With the help of such a battery checker, the operator of the apparatus is able to tell whether the condition of the battery is adequate to power the apparatus for such operations as picture taking or sound recording without risking a malfunction or failure due to a weak battery.
A variety of battery checkers is known. Some of them indicate only the no-load voltage of the battery. Such an indication does not reveal sufficient information about the condition of the battery to predict whether the battery will perform satisfactorily under a load. Other battery checkers connect a load across the battery terminals during the checking procedure. The load simulates the actual load on the battery during operation of the apparatus so that a reliable prediction of the ability of the battery to successfully power the apparatus is obtained. The present invention relates to battery checkers wherein a simulated load is applied to the battery during checking.
A serious drawback to checking a battery under load results from the fact that the checking procedure itself may drain the battery and thereby reduce its efficiency so that finally, after repeated checking, the battery can no longer be used for its intended purpose, i.e., to power the apparatus in which it is located. Such excessive drain on a battery can result from unnecessarily frequent and/or prolonged checking of the battery by the user of the apparatus. This unnecessarily frequent and/or prolonged checking may result from an over-abundance of concern on behalf of the user for the condition of the battery or merely as a result of the user amusing himself by activating the checking circuit.
In order to minimize any unnecessary drain on a battery, in a test instrument, it is known to employ a timing circuit in the test instrument to prevent the battery of the test instrument from being discharged if the main power switch is left on while the instrument is not in use (see U.S. Pat. No. 3,621,276 to Mitchell). Mitchell discloses a test instrument having a main power switch and a test switch which is momentarily closed to charge an R-C timing circuit. As long as the test switch is closed, power is applied to the test instrument. When the test switch is opened, power remains on the test instrument for a period of time determined by the R-C time constant of the R-C timing circuit. The timing circuit disclosed in the Mitchell patent does not protect against excessive drain on the instrument's battery due to prolonged closure of the test switch.
In a recently issued U.S. Pat. No. (3,879,137 to Sakazaki), an R-C timing circuit is disclosed and is purported to be effective to disconnect a battery from an exposure meter in a camera if the user should forget to open the test switch that applies power to the exposure meter. However, the circuit shown and described in the Sakazaki patent would be effective to disconnect power from the exposure meter only a predetermined time after the test switch is opened. If the test switch remains closed, the battery would continuously apply power to the exposure meter thus unnecessarily discharging the battery.